Deinking of waste paper

Details Deinking of waste paper Deinking of waste paper

2001-04-05

2003-06-10

Nguyen, Dean T. (Department: 3629)

Paper making and fiber liberation

Processes of chemical liberation, recovery or purification...

Waste paper or textile waste

C162S072000, C435S278000

Reexamination Certificate

active

06576083

ABSTRACT:

TECHNICAL FIELD
This invention relates to processes for removing inks, coatings and toners during the recycling of starch-containing waste papers using both a starch-degrading enzyme and a pectate lyase. More particularly, it relates to such processes leading to improved brightness and cleanliness of the pulp or paper.
BACKGROUND ART
In the recycling of waste paper it is usually desirable to remove the printing ink in order to produce new paper of high brightness and improved cleanliness. The term “cleanliness” relates to a lack of or a reduced amount of residual ink particles in the pulp and/or paper produced from these pulps. Some of the higher quality grades of paper including mixed office waste have seen a lower rate of reuse compare to other grades, such as old corrugated cardboard. This is due to the difficulty of removing polymeric inks, coatings and toners such as non-contact, fused laser-prints, xerographic toners, UV/EB cured inks, varnish overlays and coated paper. It is conventional to repulp (or disintegrate) the old paper together with deinking chemicals, such as deinking surfactant, NaOH and sodium silicate, combined with bleaching/brightening with hydrogen peroxide and deinking chemicals and by separation of ink particles from the pulp. However, standard chemical deinking agents may not work well for laser ink and xerographic toner removal.
Enzymatic methods have been described in the prior art to improve removal of ink and thereby increase the brightness and the cleanliness of the pulp produced from this process.
An amylase, i.e. a starch-degrading enzyme has been described in U.S. Pat. No. 5,879,509 (Novo Nordisk) to improve the deinking effect. Pectinases are disclosed in U.S. Pat. No. 5,785,809 (KRICT) to dislodge ink particles from waste paper. Furthermore, the use of endo-pectate lyase in the pulping of kôzo (Japanese paper mulberry,
Broussonetia kazinoki
Sieb) has been described by Kobayashi Y et al.(1984), Mokuzai Gakkaishi, 30, 848-56.
It is the object of this invention to provide an improved process for removal of printing ink and increasing brightness and cleanliness of the pulp and paper for use in the recycling of starch-containing waste paper.
STATEMENT OF THE INVENTION
We have found that in the production of pulp and paper from starch-containing printed paper, the deinking effect can be improved by including treatment with both a starch-degrading enzyme and a pectate lyase.
Accordingly, the invention provides a process for producing a papermaking pulp from starch-containing printed paper, comprising the following steps:
a) disintegrating the paper to produce a pulp,
b) treating with a starch-degrading enzyme and an pectate lyase during or after step a), and
c) separating ink particles from the pulp after steps a) and b).
The invention also provides a process for recycling old starch-containing printed paper into new paper or tissue, comprising producing a pulp by the above process, followed by paper- or tissue-making.
DETAILED DESCRIPTION OF THE INVENTION
In the context of the present invention the term “improved deinking effect” and “improved process,” indicates that the brightness and cleanliness of any paper produced from the deinked pulp is increased/enhanced in comparison to paper produced from pulps which have not been treated according to the present invention.
Starch-Containing Printed Paper
The process of the invention is applicable to the recycling of any kind of printed, starch-containing paper. Examples include old newspaper, magazines, mixed and sorted office waste and papers printed using laser or Xerographic methods. The paper may contain mineral fillers such as calcium carbonate and clay.
The starch used in the manufacture of these papers may consist of starch from any source and generally contains 20-30% of amylose and the balance amylopectin. Examples include corn starch, wheat starch, potato starch, rice starch and tapioca starch. When used as a coating or sizing material, the starch to be used will generally be pretreated to achieve a limited hydrolysis by cooking with amylase or acid.
The starches used in the paper manufacturing process may also consist of modified starch. Modified starches useful for paper coating include dextrin (e.g. white dextrin, canary dextrin or British gum), acid-modified starch, oxidized starch (chlorinated starch), hydroxyethylated starch and cationic starch.
The inks to be removed by the process of this invention include but are not limited to non-contact laser inks, xerographic toners, letterpress ink generally used in printing newsprint, magazine print, offset printing ink, ultraviolet or electron beam cured ink.
Disintegration
The disintegration step may be performed in a conventional pulper, typically for 5-30 minutes at 3-30% pulp consistency.
Conventional deinking chemicals typically comprise an alkaline reagent and a surfactant. The surfactant can, e.g., be used at a dosage of 0.025-0.6%, preferably 0.030-0.15%. The surfactant is preferably nonionic in nature, e.g. ethoxylated octyl or nonyl phenol or any of the nonionic surfactants disclosed in Park et al., 1992, Biotechnology and Bioengineering 39:117-120. The alkaline reagent may be NaOH (e.g. 0.2-5%, preferably 0.5-1%) and/or sodium silicate (e.g. 0.4-5%, preferably 0.5-2%). The alkaline reagents are usually added to a pH of 8-12, preferably 10-11.5. The deinking chemicals may further comprise magnesium sulfate, and hydrogen peroxide.
If the enzyme treatment is performed during or after the disintegration, it may be preferable to modify the addition of deinking chemicals (as described further below) in order to provide suitable conditions for the action of the enzyme, and particularly to reduce or avoid the addition of alkaline reagent to achieve a pH, which is suitable for the enzyme action.
Starch-Degrading Enzyme
The starch-degrading or amylolytic enzyme is preferably an amylase, e.g. an &agr;-amylase, a glucoamylase or a debranching enzyme. A single enzyme or a combination may be used, e.g. &agr;-amylase together with glucoamylase and/or a debranching enzyme. It is preferred to perform the enzyme treatment at an alkaline pH in the range 6-10, preferably 8-10 and to use an enzyme, which is alkaline stable and active in this range and preferably has optimum activity in this range.
Examples of preferred &agr;-amylases are those derived from strains of Bacillus, e.g.
B. amyloliquefaciens
(
B. subtilis
),
B. licheniformis
or
B. stearothermophilus
and from strains of Aspergillus, e.g.
A. oryzae.
Examples of commercial products are BAN™, Termamyl®, Aquazyme Ultra™ and Fungamyl™ (products of Novozymes A/S).
Glucoamylase derived from a strain of
Aspergillus niger
is preferred, e.g. the commercial product AMG (product of Novozymes A/S).
The debranching enzyme is preferably a pullulanase, particularly one derived from a strain of
Bacillus acidopullulyticus,
e.g. the commercial product Promozyme® (product of Novozymes A/S).
Suitable conditions for Bacillus amylase may be pH 4-10, 20°-90° C., preferably pH 6-10, 40°-70° C. Suitable conditions for
A. oryzae
amylase may be pH 3-8, 20°-70° C., preferably pH 5-6.
Pectate Lyase
The Pectate lyase (EC 4.2.2.2) is an enzyme which catalyse the random cleavage of &agr;-1,4-glycosidic linkages in pectic acid (also called polygalacturonic acid) by transelimination. Pectate lyases also include polygalacturonate lyases and poly(1,4-&agr;-D-galacturonide) lyases. A single enzyme or a combination of pectate lyases may be used.
It is preferred to perform the enzyme treatment at a pH of 6-10, more preferably pH 8-10 and a temperature of 25-80° C., is more preferably 35-55° C. The use of precipitated calcium carbonate in some types of papers mentioned above assures an adequate calcium ion level for the action of certain of the amylases also mentioned earlier.
Examples of preferred pectate lyases are those that have been cloned from different bacterial genera such as Erwinia, Pseudomonas, Klebsiella, Xanthomonas and Bacillus, especially
Bacillus licheniformis
(U.S. patent application No. 6,124,127

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